The present invention relates to a transverse leaf spring bearing unit with a bearing component supporting a transverse leaf spring in a motor vehicle and a transverse leaf spring arrangement for a motor vehicle with a bearing component.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Springs in the form of leaf springs are used for guiding and suspending vehicle wheels. A leaf spring is made of a resilient material such as metal and/or plastic and/or composite materials and has an elongated shape, typically a beam-shape, with a central region and at least two ends.
Wheel suspensions are employed as part of a chassis for connecting the wheels to the vehicle. Here, the wheel suspensions can be connected directly to the mostly self-supporting body. Depending on the embodiment, the wheel suspensions can also be arranged on a subframe connected to the body or on a chassis.
Light-weight and compact embodiments increasingly tend to employ a leaf spring, in particular for the rear vehicle wheel suspension. As so-called transverse leaf spring, the leaf spring is arranged horizontally and transversely to the longitudinal axis of the vehicle. In the central region, the transverse leaf spring is customarily connected to or held on the vehicle body by way of two bearing units. In this way, the two ends can perform a substantially vertical spring movement. The transverse leaf spring is operatively connected to wheel carriers or to a further component of the wheel suspension by way of end-side bearings disposed on the ends of the transverse leaf spring. The transverse leaf spring performs wheel-guiding functions, linkage functions as well as damping and load-bearing tasks and may also replace coil springs and/or stabilizers in the conventional wheel suspension.
The bearing units are designed so that the transverse leaf spring is rigidly affixed in the direction of the vertical vehicle axis, but is translationally movable in the direction of the transverse axis of the vehicle for rotation about an axis extending parallel to the longitudinal axis of the vehicle. In this way, the transverse leaf spring can be supported on the vehicle body, such that the ratio of the roll spring rate to the stroke spring rate can be adjusted, making insertion of a transverse stabilizer for stabilizing the vehicle unnecessary.
The use of transverse leaf springs becomes even more important with the increasingly light-weight construction of modern vehicles. The transverse leaf spring is installed so as to perform the functions of the body springs or coil spring as well as of the stabilizers. To take over the functions of body springs (stroke) and stabilizer (roll), the transverse leaf spring must ensure simultaneously a certain roll stiffness (resistance to opposing vertical movement of the wheels) and a certain stroke stiffness (resistance against vertical movement of the wheels in the same direction). As a result, the functions stroke spring rate and roll spring rate can be combined in a single component, a so-called integral spring. An important characteristic value is here the ratio of the roll rate to the stroke rate. This ratio must be greater than 1 so as to be able to integrate the stabilizer functions; ideally, the ratio is even 2 or greater. A large ratio between the roll stiffness and stroke stiffness ensures that the wheel suspension exhibits a high resistance to body roll of the vehicle body. At the same time, a sufficient flexibility in the vertical direction of movement is attained to provide a comfortable ride.
Fundamentally, the spring properties and the stiffnesses can be adjusted via the central bearing points, by which the transverse leaf spring is connected to the sprung mass of the vehicle. The relevant parameter is here the mutual spacing between the bearing units in the longitudinal direction of the transverse leaf spring. The roll rate can be set by way of the spacing. However, depending on the design of the chassis, only a limited ratio of roll rate to stroke rate of less than 2 is possible by varying the spacing between the bearing units. However, this is insufficient for the optimal integration of the stabilizer functions. It is therefore necessary to design the bearing technology so that the bearing units are constructed very stiff in the z-direction, but are easily movable in the direction of rotation. This objective cannot be implemented, at least not sufficiently, with conventional rubber bearings, possibly resulting in bearing rupture.
It would therefore be desirable and advantageous to obviate prior art shortcomings and to provide a transverse leaf spring bearing unit with a functionally improved bearing component for supporting a transverse leaf spring, with which a sufficiently large ratio of roll rate to stroke rate can be implemented, as well as a transverse leaf spring arrangement for a motor vehicle with such a transverse leaf spring bearing unit.